The invention relates to a device for tightening strapping bands, in particular of plastics, with an abutment and a tensioning wheel provided with a return stop which can be driven by a tensioning motor by means of a gearing, which tensioning wheel forms a tensioning channel with the abutment for the band ends to be tightened and which is arranged in a gearing block with the tensioning motor and the gearing, which is mounted as a whole in a pivoted manner around a first stationary axis in the base frame of the device and which is held by holding means which are mounted with friction on a tensioning wheel pin in its ineffective position lifted from the band end and is pivoted against the abutment under the action of a (second) pressure element when the tensioning wheel starts in the tensioning direction and the holding means loses its effective position.
A device of this type is known (EP 0664256 B1), wherein the lower band end is clamped between the base plate of the device and an intermediate wedge, while the upper band end has to be threaded between the tensioning wheel and the intermediate wedge before the tensioning wheel is pressed by means of the start-up of a spring onto the abutment and draws the upper band end over the intermediate wedge and tightens it therewith. After the tightening and possibly welding of the band ends it is necessary to ventilate the tensioning wheel with a special hand lever which is provided for this and to bring it into its ineffective position lifted from the band against the force of the strong tensioning spring, so that the device can be drawn laterally and backwards from the strapping band.
The insertion of the band ends and the ventilation of the tensioning wheel is difficult, demands force during the pressing of the hand lever and usually cannot be executed with one hand. As the band ends to be connected run through different openings of the band channel, they can only be inserted one after the other and it can easily happen that they are displaced laterally against one another in the device and that they are not exactly on top of one another during the subsequent welding and that a faulty welding results.
In a similar device (hand device CE 92 of Cyklop GmbH), not the tensioning wheel, but the abutment and the intermediate wedge are pivoted backwards with a special hand lever, so as to loosen the upper band end clamped between the profiled circumferential surface of the tensioning wheel and the intermediate wedge and to open the band channel.
A tensioning device is also known (hand device PN 6.1 of Cyklop GmbH) which serves for the tightening of strappings using steel bands, the band ends of which being closed by a closing seal after the strapping. Hereby, both band ends are drawn through the closing seal, the lower band end is placed around the closing seal and is hereby secured against being drawn out, while the upper band end is drawn over a tensioning wedge by a tensioning wheel, which wedge is pressed against the tensioning wheel by means of a spring. When the strapping shall be loosened once again before the closing of the seal, so as to correct the strapping or to tighten it further, the tensioning wheel can be reversed. Here it is also necessary, for taking the device from the tightened and closed strapping, to pivot the tensioning wedge backwards with a hand lever so as to open the band channel and to be able to draw out the device laterally from the strapping.
It is the object of the invention to form a device of the type explained in more detail above in such a manner that plastic bands having band ends immediately on top of one another can initially be inserted into an open band channel and tightened in the initial position, whereby the tensioning wheel and the abutment reach their tensioning position just by switching on the tensioning motor and tighten the strapping band and loosen themselves automatically from the strapping band after the tightening and possibly closing action, return to their initial position and open the band channel again.
This object is solved by means of the invention in that the tensioning wheel can be driven by the tensioning motor in the tensioning direction and in the opposite direction and that the return stop is a freewheel with a brake which blocks the reverse rotation of the tensioning wheel when the tensioning motor stops, but which allows a reverse rotation of the tensioning wheel when the tensioning wheel reverses, and that the tensioning wheel with its tensioning wheel swivel pin is mounted rotatably in an eccentric with friction, which itself is rotatably guided in a steering lever which is mounted in a pivoted manner around a second stationary axis at the base frame and that a freewheel which is blocked against the tensioning direction between the tensioning wheel pin and the eccentric is arranged as stop means.
This embodiment has the advantage that a special mechanism which has to be operated by hand is not necessary to loosen the tensioning wheel and the abutment from their engagement with the band ends, but that it is sufficient to switch the tensioning motor into forward gear so as to bring the tensioning wheel into its operating position and to initiate the tensioning process and to later switch the tensioning motor into reverse gear so as to lift the tensioning wheel from the abutment and to open the tensioning channel. The device can hereby be gripped and guided with only one hand, the strapping band can easily be inserted with the other hand and be drawn out again from the band channel, and for initiating the tightening process and for opening the band channel, only one push button has to be pressed at the device.
As has already been mentioned, the band ends in the tensioning channel can be immediately on top of one another, whereby the lower band end is held in a non-positive manner by the surface of the abutment while the upper band end is drawn along on the surface of the lower band end by the circumferential surface of the tensioning wheel which is provided with a profile and is thereby tightened around a package or the like. This has the advantage that both band ends on top of one another can be inserted into the open tensioning channel by one hand from one side, while the other hand holds the tensioning device and initiates the tensioning process by pressing a button.
So as to ensure a precise swivel in of the tensioning wheel and an effective tightening of the band, the first stationary axis of the gearing block and the second stationary axis of the steering lever can be arranged on different sides of the abutment, conveniently in such a manner that the first stationary axis of the gearing block is arranged in the tensioning direction in front of the abutment and the second stationary axis of the steering lever is arranged behind the abutment. By this it is achieved that the clamping angle between the abutment surface and the tangent of the tensioning wheel changes automatically during start-up of the tensioning wheel in such a manner that the clamping action exerted on the band increases with increasing band tension, but that the tensioning wheel can run without further ado in the opposite direction during the later lifting from the band ends connected to one another and loosens itself automatically from the band. The tensioning wheel is hereby guided by the eccentric and the guide lever in such a manner that it is pivoted against the abutment during a rotation of the tensioning wheel in the tensioning direction in the opposite direction and is lifted from the abutment during a rotation of the tensioning wheel in the opposite direction.
The bearing friction of the tensioning wheel pin in the eccentric should conveniently not be too large, so that the tensioning wheel can exert a sufficiently high tensioning force on the band end to be tightened. It is therefore convenient if the eccentric is under the influence of a first pressure element which strives to rotate the eccentric in the tensioning direction of the tensioning wheel. This pressure element can be a torsion spring or a spiral spring which supports the rotational movement of the eccentric or carries it out.
The second freewheel with brake is conveniently arranged in the drive shaft train of the gearing for the tensioning wheel and blocks the reverse rotation of the drive shaft train when the tensioning wheel has produced the desired band tightening and the tensioning motor stops. The brake nevertheless allows a reverse rotation of the drive shaft train when the tensioning motor reverses. By this, it is achieved that the strapping is kept under tension without loading the tensioning motor until the band ends have been connected to one another and cut, for example by means of a seal or by welding, before the tensioning wheel reverses and hereby pivots back into its initial position.
The brake at the second freewheel can be a brake disc connected to the freewheel hub, which disc runs between rigid friction elements pressed together by spring elements.
So as to pivot the tensioning wheel reliably down onto the band ends to be tightened during the start-up in the tensioning direction, a torsion spring is provided as the pressure element, which spring is wound around the pivot axis of the gearing block, which spring supports the pivoting movement of the tensioning wheel against the stationary abutment. In the vented position, lifted off from the abutment, the tensioning wheel is then held in the gearing against the action of the spring by the detent torque of the tensioning motor and/or by the freewheel stop in the gearing and by the freewheel stop in the eccentric.
It is particularly convenient if the eccentric is arranged on a band side guide element which is rotatable around the pivot pin of the tensioning wheel, which element is under the influence of the first pressure element which rotates the band side guide element in the tensioning direction so that it covers the band channel laterally when the tensioning wheel is in its tensioning position pivoted down on the abutment. This band side guide element is a sector disc which comprises a chamfer guided inwardly at its front edge in the tensioning direction. If the band ends project laterally from the band channel after having been inserted therein, they are gripped after the swivel in of the sector disc by the chamfer and are completely pressed into the band channel. During the tightening, the band ends can also not slide laterally from the band channel.
Further characteristics and advantages of the invention result from the following description and the drawings, in which a preferred embodiment of the invention is explained in detail with the help of an example. It shows: